1. Field of the Invention
The present invention relates to an automatic sheet feeding system for automatically feeding cut sheets to a recording unit for image recording on the cut sheets.
2. Description of the Prior Art
In general, recording apparatus uses a continuous sheet such as a fan-fold sheet, or separate cut sheets. In case of continuous sheet, once it is loaded, no further sheet loading is required. On the other hand, cut sheets have to be fed into the recording apparatus one by one and an automatic sheet feeding mechanism is desirable.
In such automatic sheet feeding mechanism, for example a cut sheet feeder employed in conventional printers as shown in FIG. 1, the sheet feeding is effected by rotating a feed roller 201 as by a motor, while the sheet discharge is effected by a discharge roller 204 linked with a sheet advancing roller 202 in the printer. More specifically, in FIG. 1, the sheet advancing roller 202 is linked with the discharge rollers 204 for example through an unrepresented belt whereby the latter roller is rotated by the former. In such case a cut sheet 203 is fed toward the discharge rollers 204 with the progress of the printing operation from the contact point of a first pinch roller 206 and the advancing roller 202, while sheet discharge is effected by pinching the sheet with two discharge rollers 204, There are also shown a printer 205, an automatic sheet feeder 210, a recording head 212, and a second pinch roller 214.
The sheet finally leaves the discharge rollers 204 and is discharged to a tray 208. In this operation, however, sheet jamming may occur as the lower end of the sheet 203 tends to be retained between the discharge rollers 204.
Also in case the discharge rollers 204 are rotated by the sheet advancing roller 202, they have to be rotated even during mere sheet advancement or sheet discharge, thus requiring a large motor with a significant power loss.
Also the continuous rotation of the sheet advancing roller and the discharge rollers may result in a slack or a skewed advancement of the cut sheet unless these rollers are mutually synchronized, and such synchronization leads to a complicated structure and an elevated cost of the apparatus.
In case a cut sheet feeder is adopted, it is still desirable that the operator can manually load cut sheets one by one into the recording apparatus. For this purpose there are conventionally provided an exclusive selector switch for selecting an automatic sheet feed mode and a manual sheet feed mode and an aperture for inserting a cut sheet, and the operator is required to insert a cut sheet into the aperture after the selector switch is properly manipulated. In such structure, however, there results a danger of the cut sheet being manually inserted without proper shifting of the selector switch.
Also the conventional cut sheet feeder is provided with an exclusive sheet detecting switch, and the recording apparatus controls the feeder and determines the timing of sheet feeding in response to the detection by the switch. Such method not only requires an exclusive detecting switch but also an exclusive signal processing program responding to the switch in the recording apparatus, thus increasing the load to the control system therein.
Besides such conventional cut sheet feeder is provided with a feed start switch and other switches. Such arrangement not only requires exclusive switches but again needs exclusive programs for such switches in the recording apparatus, thus increasing the load of the control system thereof.
Furthermore, such conventional cut sheet feeder is often equipped with exclusive alarm means for indicating the absence of recording sheet or sheets jamming. In such conventional feeder, exclusive programs for activating such alarm means have to be provided in the recording apparatus, thus increasing the load to the control system thereof.
Furthermore, a conventional cut sheet feeder is provided with separate switches respectively for detecting the absence of recording sheet and sheets jamming. Such structure, involving plural detecting switches, requires a complicated circuitry increasing the load on the control system of the recording apparatus.
Also the conventional cut sheet feeder is provided with an exclusive switch for detecting sheet jamming, but the presence of such a switch complicates the structure and increases the load on the control system of the recording apparatus.
Furthermore the conventional cut sheet feeder is either unable to detect the absence of recording sheets or requires an exclusive detecting switch for such detection, which inevitably complicates the structure and increases the load on the control system of the recording apparatus.
Furthermore, in the conventional structure, the recording apparatus is provided with a motor for rotating the sheet advancing roller while the cut sheet feeder is provided with a motor for rotating a sheet feeding roller or a sheet discharge roller, and these motors are simultaneously in motion for a certain period. Consequently there is required a power source of a large capacity for driving these motors.